1. Field of the Invention p This invention relates to miniature electro-mechanical relays and integrated circuit devices, and more particularly, to apparatus for rapidly and accurately testing such relays and devices in production.
2. History of the Prior Art
Electro-mechanical relays have been used in electronic circuits for as long as such circuits have been manufactured. Such relays utilize a mechanical connector which is opened and closed to make contact between two points in an electronic circuit. Although many such relays have been replaced by electronic switches which may be of microscopic size and thus fit well within modern integrated circuits, many situations exist where the electrical performance of an electro-mechanical relay is superior to that of the electronic switch. For example, an electro-mechanical relay can achieve a flat amplitude response well into the gigahertz frequency range and still have a response down to direct current. The power handling capabilities of an electro-mechanical switch greatly exceed those of electronic switches. For these and many other reasons, electro-mechanical switches are useful in many situations.
Small electro-mechanical relays are often encapsulated in very small housings and are used in various products such as aircraft. Often relays used in these products require significant testing over a wide range of temperature and environmental conditions. The testing of these parts is quite stringent because failure of the relays could have significant effect on the products with which they are used. For example, certain of these relays are tested across temperature ranges which vary from minus 65 degrees centigrade to plus 125 degrees centigrade. Among other things, the relays are tested while being subjected to intense atmospheric moisture. The relays are subjected to a number of tests for periods which extend up to two hours. Other encapsulated electrical devices such as semiconductor devices often must be similarly tested.
In order to test these encapsulated relays, it is necessary to position each relay in some sort of a special test assembly or socket which allows the relays to be isolated in environments in which the test conditions may be applied. These assemblies, like the relays, must be placed in hot and cold atmospheres and immersed in moisture for extended periods while various electrical tests are carried out. The extreme environmental conditions to which these sockets are subjected has caused drastic failure rates. For example, it has been typical for certain sockets to begin failing after as few as forty relays have been tested. Typically, each such test socket has been hand made by a process which requires approximately thirty hours of skilled labor. Since approximately 10,000 relays must be tested each day, the expense of testing and of constructing new sockets has made the relays overwhelmingly expensive.
Recently, a new test assembly has been devised which allows much more rapid and accurate testing of relays and devices which are encapsulated in similar enclosures (e.g., operational amplifiers and other integrated circuit devices). Such an assembly is designed to be easily manufactured by mass production processes, allows easy and rapid loading of devices to be tested, and gives very accurate measurements for test values applied at the base of the test assembly. Such a test assembly is described in detail in U.S. patent application Ser. No. 08/040,529, entitled Test Assembly For Relay, A. Sparling et al, filed Mar. 31, 1993, and assigned to the assignee of the present invention. However, because the points at which test instruments may be applied to measure values are at the base of the test assembly, the measurements which are produced include values of resistance, inductance, and capacitance related to the length of the conductive path through the test assembly. The measurements also are affected by the cross sectional dimensions at each connection point between the contacts of the measuring device and those of the device being tested, the length of the leads of the device being tested, and other factors unrelated to the values of the resistance, inductance, and capacitance of the relay or other circuitry residing within the enclosure. For many purposes, it is necessary to provide a very accurate test of such internal device characteristics. For example, various government acceptance tests require that resistance values across the contacts of a relay be less than one-tenth of an ohm when measured at a position one-eighth of an inch from a relay enclosure.